What Went Wrong?

Chapter 14. Testing of Trips and Other Protective Systems

The driver of a ramshackle Maputo taxi that had holes in the floor and kept breaking down was asked if all the gears worked. “Yes,” he said, “but not all at the same time.”—Daily Telegraph (London), January 7, 1995

Many accidents have occurred because instrument readings or alarms were ignored (see Sections 3.2.8, 3.3.1, and 3.3.2). Many other accidents, including Bhopal (see Section 21.1), have occurred because alarms and trips were not tested or not tested thoroughly or because alarms and trips were made inoperative or their settings altered, both without authority. These and some related accidents are described here.

Microprocessor-based control systems are being increasingly used ...